A vertical representation of soil carbon in the JULES land surface scheme (vn4.3_permafrost) with a focus on permafrost regions
A vertical representation of soil carbon in the JULES land surface scheme (vn4.3_permafrost) with a focus on permafrost regions
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DOI：
10.5194/gmd-10-959-2017
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发表时间：
2017-02-24
影响因子：
5.1
通讯作者：
Ekici, Altug
中科院分区：
文献类型：
--
作者：
Burke, Eleanor J.;Chadburn, Sarah E.;Ekici, Altug
永久冻土区碳循环的改进表示将使对未来气候-碳系统的预测更加现实。目前JULES（联合英国陆地环境模拟器）-英国地球系统模型（UKESM）的陆地表面模型-使用标准的四池RothC土壤碳模型。本文介绍了一个新版本的JULES （vn4.3_冻土），在土壤碳模型中增加了土壤垂直维度，在每个土层中设置了4个库。每一土层的呼吸速率取决于该土层的温度和湿度条件。低温扰动/生物扰动过程是土壤碳在层间转移的过程，表现为扩散混合。凋落物输入和土壤呼吸均随深度的增加而减小。该模型现在包括一个示踪剂，这样就可以通过模拟标记和跟踪选定的土壤碳。模拟结果表明，与标准版JULES （vn4.3）相比，大尺度土壤碳的水平和垂直分布有所改善。与标准版本的JULES一样，垂直离散模型仍然无法模拟冻土带地区足够的土壤碳。这在一定程度上是因为JULES低估了冻土带上的植物生产力，但也因为与永久冻土碳积累有关的所有过程，如泥炭的发展，并没有包括在模型中。与标准模型相比，垂直离散模型显示土壤呼吸在春季开始的延迟，导致在此期间净碳吸收量增加。为了提供一个更合适的冻土碳表示来量化UKESM内的冻土碳反馈，利用观测到的土壤碳初始化冻土区（1 m以下）的深层土壤碳。现在土壤碳有轻微的漂移（< 0.018% 10年（-1）），但在气候变化较小的20世纪，模拟土壤碳的变化与原始垂直离散模型相当，且明显大于漂移。
An improved representation of the carbon cycle in permafrost regions will enable more realistic projections of the future climate-carbon system. Currently JULES (the Joint UK Land Environment Simulator) - the land surface model of the UK Earth System Model (UKESM) - uses the standard four- pool RothC soil carbon model. This paper describes a new version of JULES (vn4.3_ permafrost) in which the soil vertical dimension is added to the soil carbon model, with a set of four pools in every soil layer. The respiration rate in each soil layer depends on the temperature and moisture conditions in that layer. Cryoturbation/bioturbation processes, which transfer soil carbon between layers, are represented by diffusive mixing. The litter inputs and the soil respiration are both parametrized to decrease with increasing depth. The model now includes a tracer so that selected soil carbon can be labelled and tracked through a simulation. Simulations show an improvement in the large-scale horizontal and vertical distribution of soil carbon over the standard version of JULES (vn4.3). Like the standard version of JULES, the vertically discretized model is still unable to simulate enough soil carbon in the tundra regions. This is in part because JULES underestimates the plant productivity over the tundra, but also because not all of the processes relevant for the accumulation of permafrost carbon, such as peat development, are included in the model. In comparison with the standard model, the vertically discretized model shows a delay in the onset of soil respiration in the spring, resulting in an increased net uptake of carbon during this time. In order to provide a more suitable representation of permafrost carbon for quantifying the permafrost carbon feedback within UKESM, the deep soil carbon in the permafrost region (below 1 m) was initialized using the observed soil carbon. There is now a slight drift in the soil carbon (< 0.018% decade(-1)), but the change in simulated soil carbon over the 20th century, when there is little climate change, is comparable to the original vertically discretized model and significantly larger than the drift.